1. Field of the Invention
The present invention relates to headlights, and more particularly to a headlight allowing simple adjustment of a delicate luminous intensity (or light) distribution pattern in manufacturing.
2. Description of the Background Art
Conventional headlights have been configured as follows.
(a) Light emitted from a filament placed near the focal point of a parabolic mirror is reflected by the paraboloid to form a collimated beam. A front lens adjusts the collimated beam to attain a desired light distribution pattern.
(b) Light emitted from a filament is received at a multi-surface mirror, which reflects the light frontward in a desired light distribution pattern. A front lens simply serves as a cover. Each portion of the multi-surface mirror has a size and angular arrangement determined to reflect the light incident from the filament in a predetermined direction such that the desired light distribution pattern is attained in their entirety.
The headlight is used for night traffic, so that attention should be paid not only to safety of a person utilizing the headlight but also to safety of a person driving a car coming from the opposite direction. This emphasizes a need to meticulously adjust a light distribution pattern of the headlight. The structure of a conventional headlight, however, does not allow such adjustment down to detail. Thus, to enable the meticulous adjustment of the light distribution pattern, manual work has been done, e.g., to apply a light shield to a portion of the front lens. Such manual work, however, would degrade efficiency in manufacturing, and a light distribution pattern exactly as desired would be hard to realize. Accordingly, there has been a demand for development of a headlight having a structure with which meticulous adjustment of a light distribution pattern can readily be performed in mass production.
An object of the present invention is to provide a headlight that allows easy setting of a light distribution pattern down to detail when manufacturing.
According to the present invention, a headlight projecting light frontward includes: a light source; a reflector surrounding the light source from its backside to reflect light incident from the light source frontward; and a front lens located in front of the light source and the reflector. The front lens includes at least two portions different in light transmission characteristic from each other.
Provision of the front lens having the portions different in light transmission characteristic makes it possible to determine, for each portion, a travelling direction of the luminous flux having been transmitted therethrough, and its spreading mannerxe2x80x94diverged, parallel or convergedxe2x80x94and the degree of such divergence or convergence. Thus, it becomes possible to design in advance the light distribution pattern down to detail, e.g. by increasing the number of the portions having different light transmission characteristics, changing their positions or shapes, or increasing the aforementioned degree of divergence or the like. To manufacture the headlight, a mold for injection molding, for example, can be prepared to conform to the design. Accordingly, it is possible to manufacture a headlight ensuring a desired light distribution pattern with an automated injection molding process, not relying on the manual work as in the conventional case.
Preferably, the front lens of the headlight of the present invention has a center lens in the center, and the center lens includes at least two portions having different light transmission characteristics.
Luminous flux emitted from the light source directly reaches the center lens and is transmitted therethrough. As the center lens is divided into the portions different in light transmission characteristic, the travelling direction and the spreading mannerxe2x80x94diverged, parallel or convergedxe2x80x94of the luminous flux having been transmitted through each portion can be determined independently from each other. This allows superimposition of the luminous flux transmitted through a portion of the front lens other than the center lens on the luminous flux transmitted through the center lens. As a result, it is possible to readily achieve a light distribution pattern controlled with extremely high precision.
Preferably, the at least two portions of the center lens include a portion from which the light incident from the light source is radiated with an increased degree of divergence, and a portion from which the light is radiated restricting the degree of divergence.
Provision of such portions facilitates designing of a desired light distribution pattern. For example, a light distribution pattern for illuminating far ahead, that for illuminating beneath a user""s foot in particular, and other patterns can be attained.
Preferably, the aforementioned portion from which the light is radiated restricting the degree of divergence radiates a parallel beam.
The parallel beam can be formed, e.g. by disposing a convex lens at the relevant portion and positioning the light source at the focal point of the convex lens. The parallel beam thus radiated from the center of the front lens is allowed to be superimposed on the light beam transmitted through the remaining portion. As a result, it is possible to obtain various kinds of light distribution patterns that can illuminate far ahead.
Preferably, the center lens is composed of a concentric lens and a bar lens.
With such an arrangement, of the luminous flux from the light source reaching the center lens, that incident on the concentric lens and that incident on the bar lens can be controlled independently from each other. Specifically, it is possible to select and set the travelling direction, the spreading mannerxe2x80x94diverged, parallel or convergedxe2x80x94and the degree of such divergence or convergence for each of the luminous flux transmitted through the respective lenses. As a result, the luminous flux transmitted through the center lens can be superimposed on the luminous flux not transmitted through the center lens, so that it is possible to readily achieve an extremely delicate light distribution pattern.
Of the luminous flux passing through the center lens, that having been transmitted through the concentric lens becomes a parallel beam, while that having been transmitted through the bar lens becomes a divergent beam that diverges outward. For example, by arranging the parallel beam at the upper level and the divergent beam at the lower level, it becomes possible to illuminate a wide range from beneath the user""s foot to far ahead in the travelling direction while preventing a driver of the oncoming car from suffering dazzle. Thus, with the structure described above, a headlight allowing easy designing of a light distribution pattern down to detail is obtained. It is noted that the parallel beam is obtained from the light transmitted through the concentric lens by positioning the light source at the focal point of the concentric lens.
Preferably, the aforementioned concentric lens is a Fresnel lens.
Using the Fresnel lens, it is possible to reduce the thickness of the front lens in the relevant portion. The manufacturing process is also simplified as integral injection molding is allowed.
Preferably, the headlight of the present invention further includes a cylindrical condenser lens surrounding the light source from its periphery to transmit the light incident from the light source, and a reflector surrounding the light source and the cylindrical condenser lens from their backsides to reflect the light transmitted through the cylindrical condenser lens frontward.
The cylindrical condenser lens transmits the light emitted from the light source sideward, restricting its degree of divergence. The light transmitted through the cylindrical condenser lens generally forms a parallel beam. If such a cylindrical condenser lens is not provided, in order to reflect luminous flux of the same quantity, a reflector would be required which has a size covering an area up to a crossing point with a xe2x80x9cdownsizing reference linexe2x80x9d that is an extended line of the line connecting the light source and a position where the front end of the cylindrical convex lens is supposed to be located. With provision of the cylindrical condenser lens, the light received from the light source can be condensed, so that a reflector only needs to cover an area up to the front end of the cylindrical condenser lens. This reduction in size of the reflector allows positioning of the front lens and the light source closer to each other. Therefore, using a center lens of the same diameter, the solid angle at the light source encompassing the center lens is increased. The luminous flux passing through the center lens is thus increased, so that the influence of the center lens on the light distribution pattern is increased correspondingly. The explanation about the solid angle not only applies to the center lens, but also applies to the entire front lens. Accordingly, by the downsizing described above, the at least two portions with different light transmission characteristics provided at the front lens come to have a great influence on the light distribution pattern.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.